Telecommunication networks usually use one or more end-to-end protection schemes to protect against potential failures on service providers' network(s) that might affect the services offered to end customers. In an optical telecommunication network, one protection scheme is the 1+1 protection scheme, in which a head-end optical splitter is used to split an optical signal and send duplicated copies of the optical signal into two paths (usually referred to as primary path and secondary path) for diverse path routing. The conventional 1+1 protection scheme also employs a tail-end optical switch (e.g., a 2×1 optical switch) connected to the two paths to select the copy of the optical signal from either the primary path or the secondary path. For example, if the optical network detects that the signal from the primary path is unsatisfactory (e.g., the signal power is lower than a threshold value), the secondary path is then used for communication. In this scheme, the tail-end optical switch, also referred to as the optical protection switch, can only select one path or the other, but not both.
In optical networks using reconfigurable optical add/drop multiplexers (ROADMs), additional degrees of freedom are introduced as the optical multiplexing may also be multi-stage. For example, a group of channels can be multiplexed into one single fiber employed as the primary path and another single fiber employed as the secondary path. In this case, optical protection can be applied to the whole group of optical channels by inserting the optical protection switch between the primary and secondary multiplexers. The optical protection switch, however, usually can only switch the entire group and lacks the flexibility for multi-direction multiplexing. In other words, existing approaches usually can only receive the group of protected channels from one direction or the other. Some other multi-direction multiplexer approaches, in contrast, may allow for channels to be configured as non-protected services, but still share a single common mux/demux port.